1. Field of the Invention
The present invention relates to a solid-state image sensor and manufacturing method thereof, and a camera.
2. Description of the Related Art
In recent years, a solid-state image sensor having lightguides for increasing light to be incident on photoelectric conversion portions has been proposed. As described in Japanese Patent Laid-Open No. 2004-207433, a silicon nitride film is formed on a semiconductor substrate, on which photodiodes are formed, by a low-pressure CVD (Chemical Vapor Deposition) method, an interlayer insulation film is formed on the silicon nitride film, and the interlayer insulation film is etched using the silicon nitride film as an etching stopper. Opening portions required to form lightguides are formed by etching the interlayer insulation film. Furthermore, by etching the silicon nitride film via the opening portions, opening portions are also formed in the silicon nitride film. Also, as described in Japanese Patent Laid-Open No. 2004-207433, since the silicon nitride film as the etching stopper has a high hydrogen absorption effect, hydrogen can be prevented from entering a portion covered by the silicon nitride film (paragraphs 0019 to 0021, 0030, and 0031). Furthermore, Japanese Patent Laid-Open No. 2004-207433 describes a structure in which a partial region (a surrounding region of each lightguide) of the upper face of each photodiode is covered by the silicon nitride film via a gate insulation film (paragraph 0021, FIG. 3(B)).
The silicon nitride film described in Japanese Patent Laid-Open No. 2004-207433 functions to prevent hydrogen from entering a portion covered by that film. Hence, it is understood that the silicon nitride film is a film having a small hydrogen content, that is, a silicon nitride film (to be referred to as DCS-SiN hereinafter) formed by the low-pressure CVD method using dichlorosilane (SiH2Cl2): to be referred to as DCS hereinafter). When a pixel is covered by the DCS-SiN, hydrogen supply to each photoelectric conversion portion becomes insufficient, and dangling bonds cannot be sufficiently terminated. Hence, it is difficult to obtain a solid-state image sensor with a low dark current.
On the other hand, a method of forming a silicon nitride film (to be referred to as P—SiN hereinafter) on each photoelectric conversion portion by a plasma-enhanced CVD (PECVD) method so as to increase a hydrogen supply amount to the photoelectric conversion portion has been proposed. However, with this method, since a substrate suffers plasma damages at the time of formation of the P—SiN, a structure which covers pixels by the P—SiN may increase crystal defects of photoelectric conversion portions. Hence, this method is disadvantageous to obtain a solid-state image sensor with a low dark current.